**Course Title:** Mastering C#: From Fundamentals to Advanced Programming **Section Title:** Working with Collections and LINQ **Topic:** Use LINQ to query collections and perform advanced data filtering and manipulation.(Lab topic) **Overview** In the previous topics, we introduced LINQ (Language Integrated Query) and explored its basic features for querying collections. In this lab topic, we will delve deeper into the advanced features of LINQ, focusing on data filtering and manipulation. We will learn how to use various LINQ methods to perform complex queries and transform data into the required format. **LINQ Query Methods** LINQ provides a wide range of query methods that can be used to filter, sort, and manipulate data. Here are some of the most commonly used methods: 1. **Where()**: Filters a sequence of values based on a predicate. 2. **Select()**: Projects each element of a sequence into a new form. 3. **OrderBy()**: Sorts a sequence in ascending order. 4. **OrderByDescending()**: Sorts a sequence in descending order. 5. **GroupBy()**: Groups a sequence by a common attribute. 6. **Join()**: Combines two sequences based on a common key. 7. **Take()**: Returns a specified number of contiguous elements from a sequence. 8. **Skip()**: Bypasses a specified number of elements in a sequence. **Lab Exercise 1: Filtering and Sorting Data** In this exercise, we will use LINQ to filter and sort a list of employees. ```csharp using System; using System.Collections.Generic; using System.Linq; class Employee { public string Name { get; set; } public int Age { get; set; } public string Department { get; set; } } class Program { static void Main() { List<Employee> employees = new List<Employee> { new Employee { Name = "John", Age = 25, Department = "Sales" }, new Employee { Name = "Jane", Age = 30, Department = "Marketing" }, new Employee { Name = "Bob", Age = 35, Department = "Sales" }, new Employee { Name = "Alice", Age = 20, Department = "Marketing" } }; // Use Where() to filter employees who are older than 30 var filteredEmployees = employees.Where(e => e.Age > 30); // Use OrderBy() to sort employees by age in ascending order var sortedEmployees = employees.OrderBy(e => e.Age); // Use OrderByDescending() to sort employees by age in descending order var sortedEmployeesDescending = employees.OrderByDescending(e => e.Age); Console.WriteLine("Filtered Employees:"); foreach (var employee in filteredEmployees) { Console.WriteLine($"Name: {employee.Name}, Age: {employee.Age}"); } Console.WriteLine("Sorted Employees (Ascending):"); foreach (var employee in sortedEmployees) { Console.WriteLine($"Name: {employee.Name}, Age: {employee.Age}"); } Console.WriteLine("Sorted Employees (Descending):"); foreach (var employee in sortedEmployeesDescending) { Console.WriteLine($"Name: {employee.Name}, Age: {employee.Age}"); } } } ``` **Lab Exercise 2: Grouping and Joining Data** In this exercise, we will use LINQ to group and join two lists of data. ```csharp using System; using System.Collections.Generic; using System.Linq; class Order { public int OrderId { get; set; } public string ProductName { get; set; } } class Customer { public int CustomerId { get; set; } public string Name { get; set; } } class Program { static void Main() { List<Order> orders = new List<Order> { new Order { OrderId = 1, ProductName = "Product A" }, new Order { OrderId = 2, ProductName = "Product B" }, new Order { OrderId = 3, ProductName = "Product C" } }; List<Customer> customers = new List<Customer> { new Customer { CustomerId = 1, Name = "John" }, new Customer { CustomerId = 2, Name = "Jane" }, new Customer { CustomerId = 3, Name = "Bob" } }; // Use GroupBy() to group orders by product name var groupedOrders = orders.GroupBy(o => o.ProductName); // Use Join() to combine orders and customers based on order ID var joinedData = from o in orders join c in customers on o.OrderId equals c.CustomerId select new { OrderId = o.OrderId, ProductName = o.ProductName, CustomerName = c.Name }; Console.WriteLine("Grouped Orders:"); foreach (var group in groupedOrders) { Console.WriteLine($"Product Name: {group.Key}"); foreach (var order in group) { Console.WriteLine($"Order ID: {order.OrderId}"); } } Console.WriteLine("Joined Data:"); foreach (var data in joinedData) { Console.WriteLine($"Order ID: {data.OrderId}, Product Name: {data.ProductName}, Customer Name: {data.CustomerName}"); } } } ``` **Practical Takeaways** * Use LINQ query methods to filter, sort, and manipulate data. * Use Where() to filter data based on a predicate. * Use OrderBy() and OrderByDescending() to sort data in ascending and descending order. * Use GroupBy() to group data by a common attribute. * Use Join() to combine two sequences based on a common key. **External Resources** * [LINQ documentation on MSDN](https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/linq/) * [LINQ tutorial on C# Corner](https://www.c-sharpcorner.com/article/linq-tutorial-in-csharp/) **Leave a Comment or Ask for Help** If you have any questions or need help with the lab exercises, please leave a comment below. We will respond to your questions and provide assistance as needed. In the next topic, we will cover **Reading and writing files in C# (StreamReader, StreamWriter)**.